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J B Hanson

Publications and source records attributed to J B Hanson.

At least 37 records · Page 2Linked to original sources
PubMed1979

Energy-linked Sulfate Uptake by Corn Mitochondria via the Phosphate Transporter.

Corn shoot mitochondria possess an energy-linked transport system for sulfate uptake as demonstrated by osmotic swelling and [(35)S]SO(4) (2-) accumulation. Maximum uptake is secured in the presence of Mg(2+) and oligomycin with sucrose for osmotic support. Neither phosphate nor dicarboxylate anions are required. When added simultaneously, millimolar concentrations of phosphate block [(35)S]SO(4) (2-) uptake after the initial minute. Mersalyl, N-ethylmaleimide, and 2,4-dinitrophenol are strong inhibitors of sulfate uptake; n-butylmalonate is a weak inhibitor. These inhibitors act in the same fashion on phosphate uptake. It is concluded that sulfate uptake in the absence of phosphate is by the phosphate transporter.

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PubMed1979

Energy-linked Adenosine Diphosphate Accumulation by Corn Mitochondria: I. General Characteristics and Effect of Inhibitors.

Corn mitochondria show respiration-linked net accumulation of [(3)H]ADP in the presence of phosphate and magnesium, especially if the formation of ATP is blocked with oligomycin. Inhibition of ADP-ATP exchange by carboxyatractyloside also activates ADP accumulation, and addition of carboxyatractyloside or palmitoyl-coenzyme A to oligomycin-blocked mitochondria produces additional ADP uptake. With carboxyatractyloside the accumulated ADP is phosphorylated to ATP. With oligomycin, only a little ATP is formed. Millimolar concentrations of ADP are required for maximum uptake, and the K(m) (3.77 millimolar) for ADP translocation is independent of whether oligomycin or carboxyatractyloside is used. This is not true for ADP concentrations in the 0.05 to 0.25 millimolar range. Accumulated [(3)H]ADP rapidly exchanges with unlabeled AMP, ADP, or ATP, but not with other diphosphate nucleotides or 2 millimolar substrate anions. [(3)H]AMP is not accumulated, but [(3)H]ATP is accumulated to about one-half the extent of [(3)H]ADP. Tricarboxylate substrates inhibit ADP net uptake, and inhibition by citrate is competitive with K(i) = 10 millimolar. The evidence suggests the presence of a pathway, carboxyatractyloside-insensitive and different from the translocase, which operates to maintain adenine nucleotides in the matrix.

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PubMed1979

Energy-linked Adenosine Diphosphate Accumulation by Corn Mitochondria: II. Phosphate and Divalent Cation Requirement.

The requirement for phosphate and Mg(2+) in energy-linked [(3)H] ADP accumulation by corn mitochondria has been studied. Arsenate will fully substitute for phosphate; sulfate partially substitutes; acetate, bicarbonate, and pyrophosphate are ineffective. Phosphate is also taken up by the mitochondria, but the ADP/Pi ratio varies widely with experimental treatments. ADP does not exchange with endogenous labeled phosphate, although Pi/(32)Pi exchange occurs.Mg(2+) is also accumulated during ADP uptake. Mg(2+) can be substituted with varying efficiency by other divalent cations, but not monovalent cations. Effective cations typically increase phosphate uptake, particularly Ca(2+) . Ca(2+) -activated ADP accumulation is insensitive to carboxyatractyloside over a wide range of Ca(2+) concentrations. When Ca(2+) is substituted for Mg(2+) it is not necessary to block ATP formation to secure high levels of ADP accumulation, since Ca(2+) will divert energy from ATP formation into ion uptake.It is suggested that the transport mechanism may carry out a concerted transport of ADP and phosphate with bound divalent cation. The phosphate transporter may be involved, or alternatively a special mechanism for trivalent anion transport may exist which acts cooperatively with the phosphate transporter.

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PubMed1979

Energy-linked Potassium Influx as Related to Cell Potential in Corn Roots.

Cell potentials and K(+) ((86)Rb) influx were determined for corn roots over a wide range of external K(+) activity (K degrees ) under control, anoxic, and uncoupled conditions. The data were analyzed using Goldman theory for the contribution of passive influx to total influx. For anoxic and uncoupled roots the K(+) influx shows the functional relationship with K degrees predicted with constant passive permeability, although K(+) permeability in uncoupled roots is about twice that of anoxic roots. In control roots the equation fails to describe K(+) influx at low K degrees , but does so at high K degrees , with a gradual transition over the region where the electrical potential becomes equal to the equilibrium potential for K(+) (psi = E(K)). In the low K degrees range, where net K(+) influx is energetically uphill, participation of an energy-linked K(+) carrier is indicated. In the high K degrees range, K(+) influx becomes passive down the electrical gradient established by the cell potential. Since the cell potential includes a substantial electrogenic component, anoxia or uncoupling reduces passive influx.

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PubMed1978

The effect of calcium on the respiratory responses of corn mitochondria.

Tightly coupled respiring corn mitochondria (Zea mays L.) respond to calcium addition with a transitory respiratory increase, proton extrusion, and Ca2+ binding. The extent of response is dependent upon the level of endogenous phosphate, and a large sustained respiratory increase can be obtained with addition of phosphate. However, calcium does not act as a permeant cation in that it will not penetrate with acetate. It appears that the transitory respiratory increase must be linked to the uptake of a calcium phosphate complex, but there is no evidence that transport of the complex serves to produce an electrophoretic calcium uniport. It is believed that calcium phosphate transport in corn is a constitutive property, and not produced by membrane damage.

Acetates↗
PubMed1978

Application of the chemiosmotic hypothesis to ion transport across the root.

The evidence on how ions accumulated in the root symplasm are released to the xylem vessels is examined. It is suggested that Mitchell's chemiosmotic hypothesis as applied to ion transport might account for the process. A model based on this hypothesis shows the symplasm as an osmotic unit connecting two isolated solutions, but with no significant difference in proton motive force across the unit. If it is assumed that the resistance to transport by plasmalemma uniports and antiports differs in the cortical and stelar ends of the symplasm, the model will provide for an influx of ions to the xylem. The reported properties of isolated steles suggests that the porters (carriers) do have properties in accord with the model.

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PubMed1977

Effect of phosphate and uncouplers on substrate transport and oxidation by isolated corn mitochondria.

A study was made to determine conditions under which malate oxidation rates in corn (Zea mays L.) mitochondria are limited by transport processes. In the absence of added ADP, inorganic phosphate increased malate oxidation rates by processes inhibited by mersalyl and oligomycin, but phosphate did not stimulate uncoupled respiration. However, the uncoupled oxidation rates were inhibited by butylmalonate and mersalyl. When uncoupler was added prior to substrate, subsequent O(2) uptake rates were reduced when malate and succinate, but not exogenous NADH, were used. Uncoupler and butylmalonate also inhibited swelling in malate solutions and malate accumulation by these mitochondria, which were found to have a high endogenous phosphate content. Addition of uncoupler after malate or succinate produced an initial rapid oxidation which declined as the mitochondria lost solute and contracted. This decline was not affected by addition of ADP or AMP, and was not observed when exogenous NADH was substrate. Increasing K(+) permeability with valinomycin increased the P-trifluoromethoxy (carboxylcyanide)phenyl hydrazone inhibition. Kinetic studies showed the slow rate of malate oxidation in the presence of uncoupler to be characterized by a high Km and a low V(max), probably reflecting a diffusion-limited process.The results indicate that rapid malate and succinate oxidation require the operation of both the phosphate and dicarboxylate transporters, which in turn depend on maintenance of a proton motive force across the inner membrane. In addition, phosphate can stimulate acceptorless malate oxidation by reaction with the coupling mechanism, and in uncoupled mitochondria which are depleted of substrate there is a slow rate of oxidation which appears to be limited by diffusive entry.

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PubMed1977

Pyruvate and malate transport and oxidation in corn mitochondria.

Pyruvate oxidation and swelling in pyruvate solutions by corn (Zea mays) mitochondria were inhibited by alpha-cyano-4-hydroxy-cinnamic acid, an inhibitor of pyruvate transport in animal mitochondria; however, there was no inhibition of pyruvate dehydrogenase activity, and malate and NADH oxidation were not affected. These results suggest the presence of a pyruvate(-)-OH(-) exchange transporter which supplies the mitochondrion with oxidizable substrate. Lactate appears to be transported also, but not dicarboxylate anions or inorganic phosphate. The rate of pyruvate transport was much slower than that of malate, however, and valinomycin was required to elicit appreciable swelling in potassium pyruvate.Malate oxidation contributed significantly to respiration supported by pyruvate plus malate, and malate did not act solely as a "sparker" for pyruvate oxidation. NAD(+)-malic enzyme activity was found in sonicated preparations, and comparison of O(2) consumption with CO(2) released from 1-(14)C-pyruvate indicated that transported malate was being converted to pyruvate, particularly as the malate to pyruvate ratio increased. The results suggest that pyruvate transport becomes limiting under conditions of high energy demand, but that rapid malate transport makes up the difference, supplying pyruvate via malic enzyme and replenishing losses of tricarboxylic acid cycle intermediates.

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PubMed1977

Histochemical Evidence for the Occurrence of Oligomycin-sensitive Plasmalemma ATPase in Corn Roots.

A cytochemical study has been made on the localization of ATPase activity in corn (Zea mays L.) roots. Light microscopy shows washing for 4 hours to increase the general ATPase activity in the peripheral layers of the root cortex; oligomycin and N,N-dicyclohexylcarbodiimide inhibit this activity, oligomycin being more effective. Ultrastructural studies of ATPase location show oligomycin treatment to inhibit both mitochondrial and plasmalemma ATPase, but only in the epidermis and outer cortex. Studies with lipid-soluble dyes indicate that oligomycin might not penetrate very deeply into root tissue in the time span of these experiments. It is suggested that the strong inhibition of ion absorption by oligomycin without a corresponding decline in ATP content is probably due to inhibition of ion absorption in the peripheral cell layers, thus limiting the supply of ion for symplastic transport to the uninhibited tissues.

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PubMed1977

Activation of endogenous respiration and anion transport in corn mitochondria by acidification of the medium.

Acidification of the suspending medium of corn mitochondria (Zea mays L., WF9 x Mo17) from pH 7.5 to pH 6.8 to 6.4 initiates osmotic swelling with the transportable anions citrate, sulfate, and phosphate. Swelling becomes pronounced with a combination of citrate plus sulfate or phosphate. Acidification proves to activate endogenous respiration, which is essentially zero at pH 7.5. The endogenous respiration transports citrate (in the presence of sulfate or phosphate) which then contributes to respiration and the accelerated osmotic swelling. Mersalyl will inhibit the swelling and antimycin inhibits the endogenous respiration. Magnesium appears to reduce the permeability of the membranes under the acid conditions.

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PubMed1976

Cell potentials, cell resistance, and proton fluxes in corn root tissue: effects of dithioerythritol.

Studies were made of the effect of dithioerythritol on net proton flux, potassium influx and efflux, cell potential, and cell resistance in fresh and washed corn (Zea mays L. WF9XM14) root tissue. Dithioerythritol induces equal proton influx and potassium efflux rates, decreases membrane resistance, and hyperpolarizes the cell potential. Greater effects on H(+) and K(+) fluxes are secured at pH 7 than at pH 5. Other sulfhydryl-protecting reagents produced the same responses. No evidence could be found that dithioerythritol affected energy metabolism or membrane ATPase, and proton influx was induced in the presence of uncoupling agents.We deduce that dithioerythritol activates a passive H(+)/K(+) antiport, driven in these experiments by the outwardly directed electrochemical gradient of K(+). The net effect on H(+) and K(+) fluxes is believed to reside with the combined activity of a polarized H(+)/K(+) exchanging ATPase and the passive H(+)/K(+) antiport. A model is presented to show how the combined system might produce stable potential differences and K(+) content.

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PubMed1975

The action of valinomycin in uncoupling corn mitochondria.

Valinomycin in the presence of potassium is a potent uncoupler of corn (Zea mays L.) mitochondria, eliminating respiratory control. Valinomycin produces higher steady state potassium phosphate swelling which can be reversed to give active shrinkage if mersalyl is added to block the Pi(-)/OH(-) antiporter. Respiration declines concurrently. Uncouplers accelerate the shrinkage and restore the respiration. The same results can be obtained with sodium phosphate if gramicidin D is substituted as ionophore.It is concluded that valinomycin uncoupling is the result of cyclic salt transport, with influx pumping of potassium phosphate via the Pi(-)/OH(-) antiporter and efflux pumping via a K(+)/H(+) antiporter. The result is a higher level of steady state swelling, rapid turnover of the proton gradient, and uncoupled respiration rates. The level of steady state swelling can be manipulated by varying the valinomycin or K(+) concentrations, with high concentrations favoring activation of the efflux pump.A mosaic membrane model with high resistance for proton and monovalent cation penetration to the cation(+)/H(+) antiporter is used to explain the results.

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PubMed1974

Greater Length of Ribonucleic Acid Synthesized by Chromatin-bound Polymerase from Auxin-treated Soybean Hypocotyls.

An investigation has been made of the RNA synthesized by chromatin-bound RNA polymerase from soybean hypocotyls (Glycine max var. Wayne). Polymerase activity is 4- to 5-fold higher with chromatin from tissue treated with 2,4-dichlorophenoxyacetic acid, a synthetic auxin, compared to untreated tissue. Thin layer chromatography of the RNA hydrolysis products and acrylamide gel electrophoresis of the RNA synthesized by the chromatin show that increased activity induced by 2,4-dichlorophenoxyacetic acid is due primarily to the production of longer RNA chains, with only 20 to 50% increase in the number of RNA chains. The observation that 2,4-dichlorophenoxyacetic acid treatment leads to greater rates of RNA synthesis, producing longer chains in unit time, suggests that one manifestation of auxin activity is in activation of RNA polymerase I (ribosomal RNA polymerase).

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PubMed1974

Phosphate absorption rates and adenosine 5'-triphosphate concentrations in corn root tissue.

The correlations between ATP concentration in corn (Zea mays) root tissue and the rate of phosphate absorption by the tissue have been examined. Experimental variation was secured with 2,4-dinitrophenol, oligomycin, mersalyl, l-ethionine, 2-deoxyglucose, N(2) gassing and inhibition of protein synthesis. It is concluded that ATP could be the energy source for potassium phosphate absorption, but only if the transport mechanism possesses certain properties: oligomycin-sensitivity; creation of a proton gradient susceptible to collapse by uncouplers; phosphate transport via a mersalyl-sensitive Pi(-)-OH(-) transporter; good activity at energy charge as low as 0.4; short enzymatic half-life for the ATPase or phosphate transporter; a linked mechanism for K(+)-H(+) exchange transport, possibly electrogenic.

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PubMed1974

Increase in electrogenic membrane potential with washing of corn root tissue.

Washing of corn root tissue increases the electrical potential difference, negative inside, across the membranes of epidermal cells. There is no lag period in the development of the extra potential, and the entire increase is electrogenic as evidenced by collapse with the uncoupler, (p-trifluoromethoxy)-carbonyl cyanide-phenylhydrazone.Proton extrusion by the tissue declines with washing but can be reinstituted by the addition of mersalyl, an inhibitor of the Pi-OH(-) antiporter of mitochondrial membranes.It appears that washing may enhance or augment the activity of an electrogenic ion pump, possibly a proton or cation efflux pump. In addition, there may be augmentation of an anion-OH(-) antiporter driven by the proton motive force created.

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